1. Field of the Invention
The present invention relates to a measuring apparatus and a measuring method for measuring the thickness of products such as films, layers, semiconductors, etc. The present invention especially relates to a contactless thickness measuring apparatus and a method for measuring an object's thickness without contacting the object by using interference light.
2. Description of the Related Art
In recent years, semiconductor devices manufactured using very high scales of integration have been developed. In producing such devices, it is important to maintain a high level of accuracy because such semiconductor devices have an extremely small structure. For instance, when a silicon diaphragm is formed by etching, the thickness of the diaphragm is controlled by managing the silicon etching time. However, the thickness varies depending on the etching condition. For such reasons, there is a great need for highly accurate control of the silicon thickness by monitoring the silicon thickness during the etching process.
Japanese Patent Laid-Open Publication No. Hei 2-307003 discloses a method of monitoring semiconductor etching by observing variations in the strength of interfering light which is reflected from a semiconductor layer illuminated by laser light. Another prior art method proposes measuring the thickness of a silicon layer based on light from a silicon layer which has been illuminated by a halogen light. (See, e.g., NEWS/94 Proceedings pp. 217-222).
In the first above-described method of semiconductor layer thickness measurement, it is possible to measure variations in the layer thickness; however, it is impossible to measure the absolute thickness and the layer's original thickness must be known in advance to monitor the thickness variations. In the second above-described method, the detected light is too weak, and is likely to be influenced by extraneous influences such as the roughness of the silicon surface. The apparatus is also large-sized because a specific highly stable detecting device is necessary.
"Absolute thickness" as used above and hereinafter means the thickness of an object as defined by a predetermined measurement system, e.g., twenty nanometers, etc., as opposed to relative thickness, the amount or percentage of change in the object's thickness relative to some other point on the object.